This invention relates to a safety system for machinery. In particular, the invention relates to safety equipment for a mobile wood chipping machine.
The invention will be described by way of example with reference to the use of the safety system with a mobile wood chipping machine. The system of the invention may be used with machines other than mobile wood chipping machines.
Mobile wood chipping machines are used by workmen to chip branches and parts of trees into smaller pieces for providing mulch or to make the pieces of the tree more easily transportable to other locations or for easy disposal. Such machines have a feed chute leading into a chamber where chipping discs are present and the discs are driven to cause material introduced into the chamber to be shredded or chipped into small pieces. A pair of feed rollers are present at an end of the chute spaced from a feed opening into the chute. The feed rollers convey material placed into the chute towards the chipping discs. A safety bar extends across the chute in the vicinity of the feed opening and the bar is normally pulled away from the chute to cause a drive to rotate the feed rollers and is pushed towards the chute to disengage the drive. Serious accidents have been known to occur with the use of such machines. It is usual for workmen to wear gloves and other protective clothing, and it is possible that a workman may become snared by the material being fed into the chute in which case the workman may be unable to operate the safety bar in time or may be unable to operate the bar at all and as a consequence may be drawn into the machine and injured. Furthermore, the safety bar may malfunction.
It is an object of the present invention to provide a safety system for machinery which at least minimizes the disadvantages referred to above.
According to one aspect of the invention there is provided a safety system for a machine, the system having at least one passive sensor, a sensing coil associated with the machine for detecting proximity of the passive sensor and control circuitry responsive to the sensing coil for providing a control signal for use in stopping operation of the machine.
The passive sensor may consist of a tuned circuit. Preferably the tuned circuit consists of a coil and a capacitor connected in parallel with one another. The coil may have any suitable number of turns and the turns may be wound in a spiral to present a helical or a substantially flat-shaped circular coil. The passive sensor may be incorporated in a band normally worn or carried by the machine operator. Preferably, the band is placed around a part of the machine operator""s body which might be brought into proximity to the machine. The band may be worn on the wrist of the machine operator. The operator may carry or wear more than one passive sensor.
The sensing coil may be configured as a spiral or as a number of turns of wire with a non-circular path.
The sensing coil may be placed adjacent or incorporated into the machine being used by the operator. The sensing coil may be placed adjacent those parts of the machine which are able to injure the operator. Where the system of the invention is used with a wood chipping machine, the sensing coil may be mounted to the feed chute of the machine. If necessary, the sensing coil may be insulated from the chute. The sensing coil is energised by the control circuitry and the electromagnetic field provides a control output which may then be used to cause the machine with which the safety system is associated to cease operating.